A unit cell of the phase change memory device includes an access device, and a data storage element serially connected to the access device. The data storage element can include a bottom electrode electrically connected to the access device and a phase change material layer in contact with the bottom electrode. The phase change material layer can be electrically switched between an amorphous state and a crystalline state or between various resistivity states within the crystalline state depending on an amount of current provided thereto.
When a program current flows through the bottom electrode, Joule heat can be generated at an interface between the phase change material layer and the bottom electrode. Such Joule heat can transform a portion of the phase change material layer (hereinafter, referred to as a ‘transition region’) into an amorphous state or a crystalline state. Resistivity of the transition region having the amorphous state is higher than that of the transition region having the crystalline state. Accordingly, by detecting a current flowing through the transition region in a read mode, data stored in the phase change material layer of the phase change memory device may be discriminated as a logical one (1) or logical zero (0).